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- 2018
- differential low noise amplifier
- GaAs pHEMT
- Square Kilometre Array (SKA)
- fully- integrated
- balun
- broadband
- S-band
- Electronic Science and Technology
- National Taiwan University
- Academia Sinica
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Temperature-dependent interface stability of MoO <sub/>3</sub> /GaAs(001) hybrid structures
摘要： We report on the influence of growth temperature and post-growth annealing on interface formation and film structure of thin MoO3 films on GaAs(001), which plays an important role for a future application as carrier-selective contacts or diffusion barriers in III/V-semiconductor spin- and opto-electronics or photovoltaics. Growth and post-growth annealing were performed in a manner that emulates heterostructure growth and lithographic processing. High-resolution transmission electron microscopy reveals nanocrystalline (“amorphous”) growth at temperatures up to 200 °C and a transition to polycrystalline growth at about 400 °C. Spatially resolved chemical analysis by energy dispersive x-ray spectroscopy reveals strong intermixing at the MoO3/GaAs(001) interface proceeding during both film deposition and annealing. Our results evidence the important role of intermixing occurring during the process of interface formation at the very beginning of deposition.
关键词： intermixing,temperature-dependent,interface stability,GaAs(001),diffusion barriers,MoO3,carrier-selective contacts
更新于2025-09-10 09:29:36
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Charge transport in GaAs nanowires: Interplay between conductivity through the interior and surface conductivity
摘要： The charge transport through GaAs nanowires, partially p-doped and partially intrinsic, is analyzed by four-point resistance profiling along freestanding nanowires using a multip-STM. The charge transport channel in the undoped segment is assigned to the surface conductivity, while the interior of the nanowire is the conductance channel in the p-doped segment. The convoluted interplay between conduction through the interior of the nanowire and surface state conduction is studied in detail. Measurements of the I-V curves along the nanowires provide the experimental basis for the proposed charge transport model for the transition of the conduction from the interior to the surface of the nanowire. A voltage drop along the surface state conduction channel leads to an upward shift of the band edges at the surface. This results, for higher applied voltages, in the removal of the depletion layer and an opening of a conductance channel between the interior of the nanowire and the surface states.
关键词： GaAs nanowires,surface conductivity,multip-STM,charge transport,four-point resistance profiling
更新于2025-09-09 09:28:46
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Photoconductive antennas based on epitaxial films In <sub/>0.5</sub> Ga <sub/>0.5</sub> As on GaAs (1?1?1)A and (1?0?0)A substrates with a metamorphic buffer
摘要： The terahertz (THz) wave generation by the spiral photoconductive antennas fabricated on the low-temperature and high-temperature grown undoped and Si-doped In0.5Ga0.5As films is studied by the terahertz time-domain spectroscopy method. The In0.5Ga0.5As layers were grown by molecular beam epitaxy on GaAs substrates with (1 0 0) and (1 1 1) A crystallographic orientations utilizing step-graded InxGa1?xAs metamorphic buffer. The antennas are excited by radiation of Er3+-fiber laser at 1.56 μm wavelength in two regimes: with pulse durations of 2.5 ps or 100 fs. It is found that the THz wave generation is 3–4 times more effective in the case of InGaAs-based antennas on (1 1 1)A GaAs substrates as compared to the (1 0 0) substrates. Power-voltage characteristic of the LT-InGaAs antenna up to and beyond threshold breakdown voltage are reported.
关键词： time-domain spectroscopy,terahertz wave generation,photoconductive antenna,GaAs (1 1 1)A,InGaAs,molecular beam epitaxy
更新于2025-09-09 09:28:46
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High density GaAs nanowire arrays through substrate processing engineering
摘要： GaAs nanowires (NWs) vertically aligned were successfully fabricated through substrate processing engineering. High-density vertical GaAs NWs are grown on n-type Si (111) substrate by molecular beam epitaxy. Systematic experiments indicate that substrate pretreatment is crucial to vertical epitaxial growth of one-dimensional (1D) nanomaterials. The substrates etched using diluted buffered oxide etch (BOE) were explored to improve the NW density and vertical. We also find that the substrate processing engineering strongly affect the morphology of GaAs NWs. Finally, we demonstrate fabrication of GaAs NW arrays on Si surface by field-emission scanning electron microscopy (FE-SEM). This single-step process indeed offers a simple and cost-effective way to obtain a large area of GaAs NW arrays without using e-beam lithography (EBL) and/or nanoimprint lithography (NIL) processes. This work provided a new approach for hight density NW arrays.
关键词： GaAs nanowire arrays,self-catalyzed,buffered oxide etch,molecular beam epitaxy
更新于2025-09-09 09:28:46
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Effects of barrier energy offset and gradient in extended wavelength infrared detectors
摘要： The extended wavelength infrared photodetectors are new class of III-V semiconductor heterojunction-based photodetectors that can detect incoming radiation with an energy significantly smaller than the minimum energy gap (Δ) at the heterojunction interface. Architecture of these photodetectors include a barrier-emitter-barrier epilayers sandwiched between highly doped ohmic top and bottom contact layers. An energy offset (????) between the barriers is necessary for the extended wavelength photodetection. In this work, we study the performance of extended wavelength infrared photodetectors with varying ???? and gradient of the potential barrier. Results indicate that the extended wavelength threshold varied slightly with varying both the gradient and offset. Spectral responsivity, however, increased with the increasing offset and decreased with increasing gradient.
关键词： Extended wavelength infrared photodetectors,III-V semiconductors,GaAs/AlGaAs heterostructures
更新于2025-09-09 09:28:46
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Quantum Hall stripes in high-density GaAs/AlGaAs quantum wells
摘要： We report on quantum Hall stripes (QHSs) formed in higher Landau levels of GaAs/AlGaAs quantum wells with high carrier density (ne > 4 × 1011 cm?2) which is expected to favor QHS orientation along the unconventional (cid:2)1ˉ10(cid:3) crystal axis and along the in-plane magnetic ?eld B(cid:4). Surprisingly, we ?nd that at B(cid:4) = 0 QHSs in our samples are aligned along the (cid:2)110(cid:3) direction and can be reoriented only perpendicular to B(cid:4). These ?ndings suggest that high density alone is not a decisive factor for either abnormal native QHS orientation or alignment with respect to B(cid:4), while quantum con?nement of the 2DEG likely plays an important role.
关键词： quantum confinement,high carrier density,in-plane magnetic field,quantum Hall stripes,GaAs/AlGaAs quantum wells
更新于2025-09-09 09:28:46
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Selectivity map for molecular beam epitaxy of advanced III-V quantum nanowire networks
摘要： Selective area growth is a promising technique to enable fabrication of scalable III-V nanowire networks required to test proposals for Majorana-based quantum computing devices. However, the contours of the growth parameter window resulting in selective growth remain undefined. Herein, we present a set of experimental techniques which unambiguously establish the parameter space window resulting in selective III-V nanowire networks growth by molecular beam epitaxy. Selectivity maps are constructed for both GaAs and InAs compounds based on in situ characterization of growth kinetics on GaAs(001) substrates, where the difference in group III adatom desorption rates between the III-V surface and the amorphous mask area is identified as the primary mechanism governing selectivity. The broad applicability of this method is demonstrated by successful realization of high quality InAs and GaAs nanowire networks on GaAs, InP, and InAs substrates of both (001) and (111)B orientations as well as homoepitaxial InSb nanowire networks. Finally, phase coherence in Aharonov-Bohm ring experiments validates the potential of these crystals for nanoelectronics and quantum transport applications. This work should enable faster and better nanoscale crystal engineering over a range of compound semiconductors for improved device performance.
关键词： GaAs,selectivity,selective area growth,epitaxy,InAs,III-V nanowire,molecular beam epitaxy
更新于2025-09-09 09:28:46
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InGaAs-GaAs Nanowire Avalanche Photodiodes Toward Single Photon Detection in Free-Running Mode
摘要： Single photon detection at near-infrared (NIR) wavelengths is critical for light detection and ranging (LiDAR) systems used in imaging technologies such as autonomous vehicle trackers and atmospheric remote sensing. Portable, high-performance LiDAR relies on silicon-based single-photon avalanche diodes (SPADs) due to their extremely low dark count rate (DCR) and afterpulsing probability, but their operation wavelengths are typically limited up to 905 nm. Although InGaAs-InP SPADs offer an alternative platform to extend the operation wavelengths to eye-safe ranges, their high DCR and afterpulsing severely limit their commercial applications. Here we propose a new selective absorption and multiplication avalanche photodiode (SAM-APD) platform composed of vertical InGaAs-GaAs nanowire arrays for single photon detection. Among a total of 4400 nanowires constituting one photodiode, each avalanche event is confined in a single nanowire, which means that the avalanche volume and the number of filled traps can be drastically reduced in our approach. This leads to an extremely small afterpulsing probability compared with conventional InGaAs-based SPADs and enables operation in free-running mode. We show DCR below 10 Hz, due to reduced fill factor, with photon count rates of 7.8 MHz and timing jitter less than 113 ps, which suggest that nanowire-based NIR focal plane arrays for single photon detection can be designed without active quenching circuitry that severely restricts pixel density and portability in NIR commercial SPADs. Therefore, the proposed work based on vertical nanowires provides a new degree of freedom in designing avalanche photodetectors and could be a stepping stone for high-performance InGaAs SPADs.
关键词： free-running mode,InGaAs-GaAs,single photon detection,avalanche photodiodes,near-infrared,nanowires
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE International Symposium on Radio-Frequency Integration Technology (RFIT) - Melbourne, Australia (2018.8.15-2018.8.17)] 2018 IEEE International Symposium on Radio-Frequency Integration Technology (RFIT) - A Fully-Integrated <tex>$S$</tex>-Band Differential LNA in <tex>$0.15-\mu \mathrm{m}$</tex> GaAs pHEMT for Radio Astronomical Receiver
摘要： A fully-integrated S-band high-gain MMIC low noise amplifier (LNA) with differential input and single-ended output is presented and implemented in 0.15-μm GaAs pHEMT for Square Kilometre Array (SKA) astronomical receiver. The low-loss input noise matching network is designed, and the fully on-chip LC balun is introduced between the first stage LNA core and the second stage amplifier to improve overall system noise figure. The 1-dB bandwidth of the LNA covers from 1.5 to 3.7 GHz. The measurement results demonstrate 31.8-dB gain, average in-band noise figure of 0.73 dB with DC power con- sumption of 25 mW. The chip area is 2.5 x 2 mm2. Also, a noise figure measurement method for the 3-port differential-input-to- single-ended-output amplifiers is introduced in this paper.
关键词： differential low noise amplifier,GaAs pHEMT,Square Kilometre Array (SKA),fully- integrated,balun,broadband,S-band
更新于2025-09-04 15:30:14
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Reactivity studies and structural properties of Al on compound semiconductor surfaces
摘要： The authors studied the structural properties of Al on III-V semiconductors (InAs, GaAs, and InGaAs) with the aim of creating smooth and abrupt interfaces. Growth conditions, such as the residual As content and the presence of intermediate layers, affect the structural properties of the Al and the underlying semiconductor. The authors find that an ultrathin layer of AlAs on (001) InAs drastically reduces the interface reaction and improves the epitaxial growth of Al. No such layer is necessary for interface reaction mitigation for Al deposited onto InGaAs or GaAs. The crystal orientation of Al planes grown on (001) InAs is [110], but is [111] on InGaAs or GaAs. The authors discuss the significance of the results for realization of structures for proximity superconductivity.
关键词： GaAs,InAs,Al,epitaxial growth,proximity superconductivity,InGaAs,interface reaction,III-V semiconductors
更新于2025-09-04 15:30:14